Lamba started the anti-drug drive around 6 AM and was addressing locals when a man hurled stones at her, they said.
The AAP MLA from Chandni Chowk received head injuries and was rushed to Aruna Asaf Ali Hospital, where she she was discharged after treatment.
While some party members claimed that a drug cartel operating in the area was behind the attack, other party members hinted towards involvement of a BJP leader, saying the attacker was earlier seen standing close to a sweet shop owned by BJP MLA OP Sharma.
Ashutosh claimed that the attack on Lamba was part of conspiracy and said the AAP will fight back. "She was targeted as she was the only one who got hit in the crowd. It's deep conspiracy. AAP will fight back," he tweeted.
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After the attack, Lamba tweeted, "Nashe ke khilaf ladai ka anjam... Mujh par hamla kar mera sar faad diya, khoon behne ke baawjood bhi main maidan nahi chhodungi... August Kranti diwas (This is the result of fight against drugs. They attacked me and it resulted in head injuries, but despite the attack I won't back down)."
Delhi Police has detained a man in this connection and is investigating the case.